[S390] dasd eer data format.

The struct dasd_eer_header needs the packed attribute, or there will
be 6 additional bytes of random data between the fixed header and
the variable length part of the eer data.

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>